Camshaft choice

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n3w6uy

n3w6uy

The Valley Ant
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I'm just learning on how to rebuild my engine and have got alot of great advice so far. I've a 1970 LA318, will be putting a dual plane Eddy intake with Eddy 4bbl Performer 500cfm and a Jegs dual exhaust system. My next hurdle is this: how do I choose which camshaft will be the best application?

It will be a daily driver, but around here, there are sharks at the red-n-greens and i do not want bitten.
 
The cam from the 340HP seems to be a good choice. Being that this will be a daily driver the cam is not too radical but will add enough to make reds & greens fun.
 
n3w6uy said:
I'm just learning on how to rebuild my engine and have got alot of great advice so far. I've a 1970 LA318, will be putting a dual plane Eddy intake with Eddy 4bbl Performer 500cfm and a Jegs dual exhaust system. My next hurdle is this: how do I choose which camshaft will be the best application?

It will be a daily driver, but around here, there are sharks at the red-n-greens and i do not want bitten.
Click to expand...

The way I would choose the right cam is first contact Mancini or Comp Cam and tell them honestly what your complete build is and they will recommend the right cam. Once you've recieved their recommendation float it on this site for yea's or nay's from the guys.

Terry
 
as noted above the stock 340 cam is a good choice or something close to it that is newer...

you do not want to over cam a 318..
 
I have the 340 cam in my 318 small 4bbl and duals, runs great. For a driver with stock highway gearing you probably don't want too much more. I can still get over 20 MPG highway and even with small port heads it pulls very hard to 5600.
 
That 500 cfm is fine for stock cammed and exhaust 318's, you'll want to step up to a 600 cfm carb.
A jump in gear ratio and converter to match the car/cam/gears/intended useage may be a very good idea to do.
 
How to choose a cam, or, how to ask the cam manufacturer and have enough info to ask the right questions.....

You'll need to decide how many hp and how much weight you want to move.
Then, decide what gears in the rear you'll be using. Much of those three things is decided by the purpose of the car. If you have any other restrictions, such as compession ratio, stock heads, etc, make sure you mention those as well.

My thought, (and its a thought nothing more) is that you want to keep a lower CR, low 9:1 or so. Since you are rebuilding, you will likely be boring the block, and this will automatically tend to boost CR. However, you can choose the piston that best suits your CR choice. A low CR means you'll want to stay in the shorter duration cams. Here is why:

Longer duration cams by design have more overlap. Overlap is the period of time that the intake and exhaust are both open. While both are open, cylinder pressure cannot build. This pressure is what makes power. A longer duration will "bleed off" pressure in an low compression engine.

Believe it or not, the stock cam profile in the 318 isn't too bad as far as cams go. It'll work fine with a bit more compression, and will make decent power. But why stop at "decent"? The reproduction 340 cam is a very nice cam, and will produce a slight lope in a 318. Its (IIRC) 268/276 (StoS), and .444" lift.

And here is the second part of cams: lift. If the stock cam had a bit more lift, it would be a great cam. But it doesn't, so its not the solution to your quest. The 340 cam has that bit of extra lift. But, don't eliminate slightly smaller cams without doing a bit of research, or asking questions. On a given duration pair of cams, the one with a slightly higher lift will show a bit more power at the peak.

Thats the simple version of how cams work. Unless you plan to get a custom grind, picking a cam based on lift and duration is the best way to go about it. This is because most cams are "pre packaged" in certain specs. You can do things with the cam centerline, lobe centerline, lift, lobe profile, etc. But all of this is stuff you really won't need to worry about on the street in a 318.

So my ideal 318 build would be:

9.5:1 CR, 340 cam, dual plane intake, 600cfm carb, 360 heads, 1.88 intake 1.70 exhaust, ported and port matched, headers, 2.25" exhaust.

A quick run on DD2k suggests you could make nearly 350/350 hp/tq from a "mild" 318.
 
I have a tough time believing you are going to get 350hp out of a 318 with a 340 camshaft. My 340 barely makes that with a stock set of X heads, headers, LD340 and a 750 Vac Sec Holley.

By the time the heads are ported and done, you'd be in a boatload of cash in cast iron parts. Money better spent on aluminums.

I think this is one case where the DD and Camquest are a bit on the happy side.

Here's an example of why I think the software is happy.

360, kb107's about 9:1, 360 heads 1.94 valves, pocket clean up, XE268H, LD340, 750DP, 1 5/8 headers. Made 350hp and 400tq. Bigger valves, but not to large, more cam and more cubes. The car at the track, runs a MPH consistent with the dyno figures.

If the heads were ported for better flow characteristics, then we'd expect a gain in power. That's a real world build that was done on a dyno that isn't happy like some of the magazines use.


The 340 cam is a good choice for a 318.
 
The software may be "happy", no doubt. However, the 318 made 320ftlbs from the factory in pre emissions trim. A boost of 30ftlbs on similar compression isn't a huge leap. Also, hp would come up significantly if measured at peak, rather than the shaved numbers the auto companies used. Two outstanding examples would be the hemi at 425hp (it was measured at 4500rpm IIRC) and the 340, which NHRA factored in at over 300hp, rather than the 275hp the factory claimed.

As to the porting, I'm not sure what the cost of a complete (valves and hardware) set of aluminum head would be, nor am I certain that they would be a huge advantage on the street. I do know that cast iron heads work well on a the street, and a mild porting job can be done at home for little more than the cost of the cutters and the die grinder. If the build is a low buck affair, as this one seems to be, all the little inexpensive tricks can add up to a healthy advantage at the light. Porting, windage tray, degreeing the cam all cost little, but can be a serious value in the $ per hp game.

I believe that 350/350 may be optimistic, but can be done. What I think most people miss is the fact that cylinder pressure is the key. If we could assume that the heads would seal perfectly against infinite pressure, a smaller cam could produce more power, particularly at low RPM.
 
Desktop Dyno 2000 I'm fairly sure they have an update since then, and I know there are other similar pieces of software.
 
The desk top dyno is an excellent program to learn and gain some understanding of how things are effected by the changes you enter into the program. From what I remember reading of them vs. actaul dyno runs is there a bit "Happy" in the HP departmen. (The program gives you more.)

Also, no matter what build you do, for the street, use the dual plane intake choice. The single plane choice is not accurate. A 50+ hp gain on nearly stock engines just doesn't happen.
 
I'd stay with the 340 cam or the comp 268/454 grind. Summit also advertises their brand of cams with similar specs very economically priced.. I'd also swap out the valve springs with the MP 249 springs..

Bob
 
Lunati Voodoo line is a good choice also. I'm building a similar 318 (Performer intake, ThermoQuad carb, #302 heads, stock ex. manifolds, dual exhaust) and my current cam choice is the Voodoo 256/262 (213/220* duration @.050", .454/.475" lift, 112* LSA). Pretty low duration so I retain good low-end torque for gas mileage and compatibility with the 2.76:1 rear gears, but lift that will keep it pulling all through the RPM's to redline (which for me will be around 5500-6000 RPM).

EDIT: I know member "Ramcharger" has this same cam in his built 360 for his truck and he has said good things about it.
 
furz4 said:
I have the 340 cam in my 318 small 4bbl and duals, runs great. For a driver with stock highway gearing you probably don't want too much more. I can still get over 20 MPG highway and even with small port heads it pulls very hard to 5600.
Click to expand...


Any idea of a part number/specs for the stock 340 cam, or better yet a website that i could actually see it at.

Edit: Found it, just when I was giving up, COMP cams came through!
 
Need a bit more info. Max340 has it right. The wilder the cam, the more the engine will need more compression and more rear gear. Off hand, the 340 cam ought to work well for what I understand you're planning.

The stock 318 heads are good for 5500 rpm without porting. When looking at cams, make this the top end of the range for those that make your short list.
 
depending on compression I would say xe262 or xe268 would be nice cams
 
In my Duster, I run a 318 with a 600 Holley, Hooker headers, stock heads, stock compression, and a Comp XE268 cam. With a stock converter and gears, it did well. With a new Hughes 2400-2500 stall TC, it revs a bit faster. This is all with a 3.21 gear. Next in line is a 3.73 gear to wake it up even further.
 
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